The conventional antitumor agents in chemotherapy are mainly classified into a group of antibiotics (for instance Adriamycin) and a group of antimetabolites (for instance 5-fluorouracil). Each group relatively has a feature of a concentration dependence drug and a time dependence drug, and both groups have a problem of being toxic to normal cells. Recently, along with the progress of surgical treatment techniques, expectations for chemotherapy, especially for an antitumor agent whose side effects are minimized, are increasing.
Strong physiological activity of organic silicon compounds has been found by Voronkov et al of Russia (silatrane), and have been investigated in detail. However, sometimes some kinds of silatrane are strongly toxic in accordance with species of substitution group, and some of them have more strong toxicity than hydrocyanamic acid or strychnine. Recently, a group comprised of Shin-etsu Chemical Products Co., Ltd, and Keio University have investigated antineoplastic features of various kinds of organic silicon compounds, and have proceeded with development of relatively low toxicity and high activaty antitumor agents (Chemical Society of Japan, 1990, No. 5, 566-574).
Inventors of this invention have already developed new antitumor agents of ring and chain compounds including silicon and nitrogen (hereafter; shortened to silamine compounds) by investigating thoroughly the antitumor features of silamine compounds (Japanese Patent Application 157518/94 and 157519/94).
However, although the toxicity of these silamine compounds are weaker than that of the antitumor agents such as Adriamycin, its antitumor activity is about 1/10, and said lower antitumor activity is pointed out as a problem.
The object of this invention is to solve the above mentioned problem of silamine compounds, and to provide a new antitumor agent of lower toxicity and high effectiveness.